Lighting device, display device and television receiver

ABSTRACT

An object is to provide a lighting device with improved workability in assembling a light guide plate, a display device and a television receiver using this lighting device. The lighting device according to the present invention has LEDs  16 , an inclined surface  32 A to which light from the LEDs  16  enter, a light exit surface  31  which emits the light, and a light guide plate  30  with the light exit surface having a rectangular shape in a planar view. The light guide plate  30  has the inclined surfaces  32 A and  32 B inclined in a form protruding outside the light guide plate  30  in one direction of the light exit surface  31 , as both side surfaces in the one side direction of the light exit surface  31  get closer to the side of the light exit surface  31 . The inclined surfaces  32 A and  32 B on the both sides have symmetrical shapes with each other. One of the inclined surfaces  32 A and  32 B is a light entrance surface and is facing a luminous surface  16   a  of the LED  16.

TECHNICAL FIELD

The present invention relates to a lighting device, a display device anda television receiver.

BACKGROUND ART

In recent years, a thin-type display device, such as a liquid crystalpanel or a plasma display panel, is used as a display device for animage display device. This usage enables the thin image display device.When the liquid crystal panel is used as the display device, the liquidcrystal panel does not emit light itself. Therefore, a lighting device(backlight unit) is separately required.

A known example of the lighting device is disclosed in PatentDocument 1. This lighting device includes LEDs (light sources) and lightguide plates. The LEDs are arranged on the side edge of the lightingdevice. The light guide plates cause light from the LEDs to be emittedtoward the display surface of the liquid crystal panel. Morespecifically, the LEDs are arranged toward the light entrance surface ofthe light guide plates. The light entered from a light entrance surfaceis guided by repeatedly being totally reflected in the light guideplate, and is emitted from a light exit surface.

-   Patent Document 1: Japanese Unexamined Patent Publication

Problem to be Solved by the Invention

In the above-described lighting device of Patent Document 1, when thelight guide plates are mounted, the light exit surface needs to bearranged in a predetermined direction (for example, on the side of theliquid crystal panel). Thus, the light guide plates need to be mountedwith attention to the orientation of the light exit surface of the lightguide plates, thus leaving room for improvement.

In a known lighting device, a plurality of light guide plates isarranged in matrix. Alight source is arranged for each light guideplate, and each light source is independently controlled to be driven.Then, brightness of light from each light guide plate can be controlled.As a result, on the light exit surface of the lighting device,brightness can be controlled for each area corresponding to each lightguide plate, thus acquiring a high display quality (so-called a localdimming technique).

In the configuration including the plurality of light guide platesarranged as described above, a light source may be arranged betweenadjacent light guide plates. In this configuration, to keep the area forarranging the light source, a space may be generated between theadjacent light guide plates. Thus, a dark section is generated in aposition corresponding to this space, and the uniformity of lightdecreases, thus causing uneven brightness. As a result that theplurality of light guide plates is arranged in matrix, the total numberof light guide plates to be used increases, and the workability inassembling the light guide plates is decreased.

DISCLOSURE OF THE PRESENT INVENTION

The present invention was made in view of the foregoing circumstances.An object of the present invention is to provide a lighting device withimproved workability in assembling light guide plates. Another objectthereof is to provide a display device and a television receiver, whichinclude this lighting device.

Means for Solving the Problem

To solve the above problems, according to the present invention, thereis provided a lighting device including: alight source; and a lightguide plate having a light entrance surface through which light from thelight source enters and a light exit surface through which the lightexits, the light exit surface having a rectangular shape in a planarview. The light guide plate has side surfaces at ends of one of sidesthereof, the side surfaces being configured as inclined surfaces thatare inclined toward the light exit surface of the light guide plate suchthat an end of the inclined surface on the light exit surface side isouter than another end of the inclined surface, and one of the inclinedsurfaces is configured as the light entrance surface that faces a lightemitting surface of the light source.

The light entrance surface needs to be arranged toward a side of theemitting surface of the light source in order to make the light from thelight source enter the light guide plate. The light exit surface needsto be arranged toward this predetermined direction in order to emitlight from the light guide plate toward the predetermined direction.That is, when the lighting device is assembled, the direction of thelight guide plate with respect to the light source needs to be alignedwith the predetermined direction.

In the present invention, of side surfaces of the light guide plate, twoside surfaces are inclined. The inclined surfaces are inclined towardthe light exit surface of the light guide plate in one side direction ofthe light exit surfaces, as getting closer to the side of the light exitsurface. Accordingly, in the light guide plate, the light exit surfaceand the surface opposite to the exit surface have different sizes, thusresulting easy distinguishing between both surfaces, as compared to aconfiguration where the light exit surface and its opposite surface havethe same size (for example, the light guide plate has a rectangularparallelepiped shape). This results in preferable workability inarranging the light exit surface toward a predetermined direction.

The inclined surfaces on the both sides may have symmetrical shapes withother. In this configuration, the same optical characteristic can beobtained (for example, refraction of the light at the light entrancesurface), when whichever surface of the both inclined surfaces is usedas the light entrance surface. That is, when the light guide plate isarranged, either one of the two inclined surfaces may be arranged towardthe light source. This realizes an easy operation for setting thedirection of the light guide plate with respect to the light source, ascompared to a configuration where only one surface of the light guideplate is selected and arranged toward the light source.

In the above configuration, the lighting device may further include atransmission scattering member configured to transmit and scatter lightin the light guide plate such that the light exits from the light exitsurface, and the transmission scattering member being arranged withlower distribution density in an area of the light exit surface closerto the end of one of sides on the light source side than in an area ofthe light exit surface around a center with respect to the one of sides.

According to this configuration, the light in the light guide plate canbe emitted from the light exit surface by the transmission scatteringmember. According to the present invention, when the light entrancesurface is inclined in a form protruding outside the light guide plate(side of the light source) in one side direction of the light exitsurface, as getting closer to the light exit surface side, the lightentered the light entrance surface is easily refracted toward the lightexit surface. As a result, on the end part of the light exit surface onthe light source side (light entrance surface where light enters), lighttends to have a small incidence angle with respect to the light exitsurface, thereby increasing the amount of light not totally reflected(light to be emitted). Thus, it can be assumed that a large amount oflight is emitted on the end part of the light source side.

In the present invention, the transmission scattering member beingarranged with lower distribution density in an area of the light exitsurface closer to the end of one of sides on the light source side thanin an area of the light exit surface around a center with respect to theone of sides. By this setting, it is possible to lower an amount oflight exit on the end part on the light source side of the light exitsurface. Even when light is made incidence on the inclined lightincidence of the present invention, an amount of light emitted on theend part of the light source side is prevented from being higher thanthat on the center. This can prevent uneven brightness. According to thepresent invention, the distribution density on the end part of the lightsource side is simply lower than the distribution density on the centerside. For example, the transmission scattering member may not be formedon the end part of the light source side, and may be formed only on thecenter side.

The transmission scattering member may be formed of a dot patterns.According to this configuration, an aspect (area, arrangement interval)of the dots is set, thus enabling to easily set the distribution densityof the transmission scattering members.

The light guide plate may have an elongated shape extending in adirection intersecting the one side direction of sides of the light exitsurface, and the light source may include a plurality of light sourcesarranged along the direction intersecting the one of sides of the lightexit surface. According to this configuration, the plurality of lightsources is individually turned on, thereby controlling the brightnessdistribution in a direction intersecting one side direction of the lightexit surface. Further, for example, as compared to a configuration wherea plurality of light guide plates is aligned in a direction intersectingone side direction of the light exit surface, the total number of lightguide plates is decreased, thus resulting in preferable workability inthe arrangement. It is to be noted that the “direction intersecting theone side direction of the light exit surface” may, for example, be the“direction along a plane direction of the light exit surface andintersecting the one side direction of the light exit surface”.

The lighting device may further include a chassis housing the lightsource and the light guide plate. The light source may include aplurality of light sources and the light guide plate may include lightguide plates arranged along a bottom plate of the chassis. The lightguide plates may be arranged such that the inclined surface of one ofthe adjacent light guide plates is opposite the inclined surface of theother one of the adjacent light guide plates. The light sources may bearranged in light source arrangement area between the inclined surfaceof the one of the adjacent light guide plates and the inclined surfaceof the other one of the adjacent light guide plates.

Accordingly, the light source is arranged in the light sourcearrangement area formed between the two adjacent light guide plates, ofthe plurality of light guide plates arranged along the bottom plate ofthe chassis. In this configuration of the lighting device, it ispossible to have a small interval in a direction intersecting thesurface (bottom surface) of the bottom plate of the chassis. That is, itis possible to realize a local dimming technique and also possible torealize the thin lighting device, by aligning the plurality of lightguide plates.

This light source arrangement area is formed by making the inclinedsurface of one light guide plate face the inclined surface of the otherlight guide plate. According to this configuration, the light sourcearrangement area can have a smaller upper end side (side close to thelight exit surface) than that, for example, in the configuration havingthe light source arrangement area formed between two parallel surfaces.That is, in a planar view, the interval of the light exit surface inboth the light guide plates can be made smaller, thus preventing unevenbrightness generated in the space between the light exit surfaces.

The lower end side (side far from the light exit surface) of the lightsource arrangement area is formed large. Thus, for example, it is easyto have a large light source arrangement area, as compared to aconfiguration where only one of two surfaces is inclined (two facingsurfaces) forming the light source arrangement area. This prevents heatgenerated when the light source is turned on from being remained, andsuppresses the temperature from being raised in the light source, thusenhancing the operational reliability.

If the light source arrangement area is formed between the inclinedsurfaces, the lower end side (side far from the light exit surface) ofthe light source arrangement area can be formed larger than that of aconfiguration where only one of two surface is inclined (two facingsurfaces) forming the light source arrangement area. Therefore, thelarge light source arrangement area can be formed easily. Accordingly,it is possible to prevent heat generated when the light source is turnedon from being remained in the light source arrangement area. This cansuppress the temperature from being raised in the light source, and canenhance the operational reliability.

The lighting device may further include at least one diffuser platecovering the adjacent light guide plates from both sides of the lightexit surface. Accordingly, in the lighting device, it is possible toobtain the even brightness between a position corresponding to the lightexit surface of the light guide plate and a position between the lightguide plates, and to prevent a dark section from being generated in aposition between the light guide plates.

The light source may be a light emitting diode. The power consumptionmay be lowered by using the light emitting diode.

A light reflection member reflecting the light from the light sourcetoward the light exit surface may cover a surface opposite to the lightexit surface on the light guide plate. According to this configuration,the light emitted toward the reflection member can be reflected againtoward the light exit surface by the light guide plate, thus enhancingthe light use efficiency.

To solve the above problems, according to the present invention, thereis provided a display device including: the above-described lightingdevice; and a display panel configured to provide display using lightfrom the lighting device.

The display panel may, for example, be a liquid crystal panel. Thisdisplay device, as a liquid crystal display device, may be applied tovarious usages, such as a television or a desktop screen of a personalcomputer, and is particularly preferable for a large screen.

To solve the above problems, the television receiver of the presentinvention may include the display device.

Advantageous Effect of the Invention

According to the present invention, there are provided a lighting devicewith improved workability in assembling a light guide plate, or a thinlighting device configured to perform local dimming, and a displaydevice and a television device using this lighting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a schematic configurationof a television receiver according to a first embodiment of the presentinvention;

FIG. 2 is an exploded perspective view showing a schematic configurationof a liquid crystal display device included in the television receiverof FIG. 1;

FIG. 3 is a plan view showing a configuration of a backlight unitincluded in the liquid crystal display device of FIG. 2;

FIG. 4 is an enlarged view showing an enlarged part of FIG. 3;

FIG. 5 is a cross sectional view showing a cross sectional configurationalong a short side direction of the liquid crystal display device ofFIG. 2 (a cross sectional view taken along a line A-A of FIG. 4);

FIG. 6 is a plan view showing alight exit surface of alight guide plate;and

FIG. 7 is an enlarged cross sectional view showing an enlarged part nearan LED in FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

An embodiment of the present invention will be described with referenceto FIGS. 1 to 7. In a part of each illustration, an X-axis, a Y-axis,and a Z-axis are shown. Each of the axial directions is commonrespectively among the illustrations. The upper side shown in FIG. 5 isthe front side, while the lower side therein is the back side.

As shown in FIG. 1, a television receiver TV according to the presentembodiment includes a liquid crystal display device 10 (display device),front and back cabinets Ca and Cb housing so as to sandwich the liquidcrystal display device 10 therebetween, a power source P, and a tuner T.A display surface 11 a is supported by a stand S, along a verticaldirection (Y-axis direction), for example. The liquid crystal displaydevice 10 has a horizontally long square shape as a whole. As shown inFIG. 2, the liquid crystal display device 10 includes a liquid crystalpanel 11 as a display panel, and a backlight unit 12 (lighting device)as an external light source. The liquid crystal panel 11 and thebacklight unit 12 are held integrally with a frame-shaped bezel 13 (seeFIG. 5).

The liquid crystal panel 11 and the backlight unit 12 included in theliquid crystal display device 10 will be described in order. The liquidcrystal panel 11 (display panel) has a rectangular shape in a planarview, and includes a pair of glass substrates bonded to each other witha predetermined gap therebetween and in which liquid crystals areenclosed. One glass substrate includes switching components (forexample, TFTs) connected to source lines and gate lines that areorthogonal to each other, pixel electrodes connected to the switchingcomponents, alignment films, and the like. The other glass substrateincludes color filters, counter electrodes, alignment films and thelike. In the color filters, coloring sections such as R (red), G(green), B (blue) are arranged in a predetermined alignment. Apolarizing plate 11 b is formed on the outer surface of both electrodes(see FIG. 5).

The backlight unit 12 will be described in detail. As shown in FIGS. 2and 4, the backlight unit 12 includes a chassis 14, optical members 15,LEDs 16 (Light Emitting Diode), an LED board 17, and a light guide plate30. The chassis 14 is formed in an approximately box-like shape havingan opening toward the front side (on the side of the liquid crystalpanel 11, the light exit side). The optical members 15 are arranged tocover the opening of the chassis 14. The LEDs 16 as light sources arearranged in the chassis 14. The LED board 17 has the LEDs 16 mountedthereon. The light guide plate 30 guides light emitted from the LEDs 16to the optical members 15. As shown in FIG. 5, the backlight unit 12includes a receiving member 19 and a holding member 20. The receivingmember 19 receives diffuser plates 15 a and 15 b constituting theoptical members 15 from the back side. The holding member 20 holds thediffuser plates 15 a and 15 b from the front side.

The chassis 14 is formed of metal, and as shown in FIG. 5, includes abottom plate 14 a, a side plate 14 b, and a receiving plate 14 c. Thebottom plate 14 a has a rectangular shape like the liquid crystal panel11. The side plate 14 b rises from the outer end of each side of thebottom plate 14 a. The receiving plate 14 c protrudes outward from therising end of each side plate 14 b. The chassis 14 is formed in anapproximately shallow box-like shape (approximately shallow dish-likeshape) opened toward the front side, as a whole. The chassis 14 has itslong-side direction aligned with the horizontal direction (X-axisdirection), and has its short side direction aligned with the verticaldirection (Y-axis direction). On each receiving plate 14 c of thechassis 14, the receiving member 19 or the holding member 20 can bemounted from the front side. On the receiving plate 14 c, the bezel 13,the receiving member 19, and the holding member 20 are fixed withscrews.

As shown in FIG. 5, the optical member 15 intervenes between the liquidcrystal panel 11 and the light guide plate 30. The optical member 15includes the diffuser plates 15 a and 15 b arranged on the side of thelight guide plate 30 and the optical sheet 15 c arranged on the side ofthe liquid crystal panel 11. The diffuser plates 15 a and 15 b areformed of a number of diffusing particles dispersed in a transparentresin base substrate with a predetermined thickness, and have a functionof diffusing transmitted light. Two of the diffuser plates 15 a and 15 bhave an equal thickness and are laminated on top of each other. Theoptical sheet 15 c has a thickness thinner than those of the diffuserplates 15 a and 15 b, and three of the optical sheet 15 c are laminatedon top of each other. In the present embodiment, the optical sheet 15 cis formed of three sheets such as a diffuser sheet, a lens sheet, and areflection-type polarizing sheet in this order from the side of thediffuser plates 15 a and 15 b (back side). The configuration of theoptical sheet 15 c is not limited to the above, and may be changedappropriately. For example, of the diffuser sheet, the lens sheet, andthe reflection-type polarizing sheet, only one of the sheets may beused, and the number of sheets to be used may possibly be changed.

The receiving member 19 is arranged on the outer periphery end of thechassis 14, and configured to receive the outer periphery end of thediffuser plates 15 a and 15 b almost entirely. For example, as shown inFIG. 5, the diffuser plat 15 a of the front side is provided on a step19 a formed on the inner end of the receiving member 19. As shown inFIG. 3, the holding member 20 is arranged on the outer periphery end ofthe chassis 14, and has a width sufficiently smaller than the short sideof the chassis 14 or the diffuser plates 15 a and 15 b, thereby locallyholding the outer periphery end of the diffuser plate 15 a.

As shown in FIG. 5, the holding member 20 has a holding piece 20 aextending into the chassis 14. The backside surface of this holdingpiece 20 a is configured to hold the diffuser plate 15 a, while thefront side surface thereof is configured to receive the liquid crystalpanel 11 through a buffer member 20 b. The holding member 20 has aprotrusion 20 c configured to fit into a concavity 19 b formed in thereceiving member 19. The protrusion 20 c fits into the concavity 19 b,thereby positioning the holding member 20.

In the backlight unit 12 according to the present embodiment, the LEDs16 are arranged on the side edge of each light guide plate 30.Configurations of the light guide plate 30 and the LED 16 will bedescribed. The light guide plate 30 has a rectangular shape elongated inan X-axis direction in a planar view, as shown in FIGS. 3 and 4, andshort side direction thereof is parallel to the short side direction(Y-axis direction, vertical direction) of the chassis 14, while the longside direction is parallel to the long side direction (X-axis direction,horizontal direction) of the chassis 14. The light guide plates 30 arealigned in a plurality of rows (nineteen rows in the present embodiment)in the Y-axis direction on the bottom plate 14 a of the chassis 14. Thelight guide plates 30 are aligned in the Y-axis direction, where each ofthe LEDs 16 is arranged between the light guide plates 30 (light sourcearrangement areas 36) in a plurality of rows in the X-axis direction.

The LED 16 is surface-mounted on the LED board 17, as shown in FIGS. 4and 5. The LED 16 has approximately a block shape as a whole, and is aside-surface light emission type device whose side surface adjacent tothe mounted surface (bottom surface in contact with the LED board 17) onthe LED board 17 is a luminous surface 16 a. The LED 16 has a light axisLA arranged along the Y-axis direction. More specifically, the lightaxis LA of the LED 16 is arranged in a direction parallel to the displaysurface 11 a of the liquid crystal panel 11 or a light exit surface 31of the light guide plate 30. In other words, the light axis LA isaligned with the short side direction of the chassis 14 (direction alongthe bottom plate 14 a of the chassis 14), that is, aligned with thevertical direction. The light emission direction (light emissiondirection from the luminous surface 16 a) is oriented upward in thevertical direction.

The light emitted from the LED 16 spreads three-dimensionally in aradial pattern within a predetermined angle range at the center of thelight axis LA, and its directivity is higher than, for example, acold-cathode tube. That is, the LED 16 has an emission intensityindicating an angular distribution in which the intensity is remarkablyhigh in a direction along the light axis LA, and in which the intensitydramatically decreases as the inclined angle with respect to the lightaxis LA increases.

The LED 16 includes a plurality of LED chips as light emitters that aresealed inside the housing a resin member. This LED 16 includes, forexample, three kinds of LED chips with different dominant emissionwavelengths. Specifically, the respective LED chips monochromaticallyemit lights of R (Red), G (Green), and B (Blue). The proximal side ofthe LED 16 is soldered onto a land of the LED board 17.

The LED board 17 is formed of a synthetic resin with a white frontsurface (including s surface facing the light guide plate 30) withexcellent light reflectivity. As shown with a dashed line of FIG. 4, theLED board 17 has a rectangular plate shape extending in the X-axisdirection in a planar view and a long side dimension thereof issubstantially equal to a long side dimension of the bottom plate 14 a.The bottom plate 14 a has an installation hole (not shown) penetratingin a predetermined position therein to fix the LED board 17 with ascrew.

The LED board 17 has a wiring pattern (not shown) formed of a metalfilm, and has a plurality of LEDs 16 mounted in predetermined positions.This LED board 17 is connected to a non-illustrative control board toreceive electricity necessary for turning on the LEDs 16 therefrom, andis configured to control driving of the LEDs 16. The LED board 17 hasthe plurality of LEDs 16 provided thereon and aligned along the longside direction thereof. The LED board 17 has a photosensor (not shown)provided thereon as well as the LEDs 16. This photosensor detects anemission state of each LED 16, thus realizing feedback control of eachof the LEDs 16.

As shown in FIG. 5, the light guide plate 30 has a symmetrical shapeabout an axis of symmetry L1 passing through the center position of theshort side direction (Y-axis direction) as a whole, and has atrapezoidal shape in a cross sectional view. The light guide plate 30 isformed of substantially transparent (capable of excellent lighttransmission) synthetic resin materials (for example, polycarbonate)whose refraction index is sufficiently higher than air.

Of the surfaces of the light guide plate 30 facing the front side, thatis, the substantially entire surface area facing the diffuser plate 15 bis the light exit surface 31 having a rectangular shape (square shape)in a cross sectional view. The light exit surface 31 is substantially asmooth surface, and is about parallel to plate surfaces (or the displaysurface 11 a of the liquid crystal panel 11) of the diffuser plates 15 aand 15 b. Of the side surfaces of the light guide plate 30, both sidesurfaces in one side direction (Y-axis direction) of the light exitsurface 31 are inclined surfaces 32 oriented toward the LEDs 16.

The inclined surfaces 32 are inclined in a form protruding outside thelight guide plate 30 in the Y-axis direction, as getting closer to thelight exit surface 31. That is, on the light guide plate 30, the leftinclined surface 32 (identified by a reference symbol 32A) shown in FIG.5 is inclined in a form protruding toward the left side of FIG. 5, asgetting closer to the light exit surface 31, while the right inclinedsurface 32 (identified by a reference symbol 32B) show in FIG. 5 isinclined in a form protruding toward the right side of FIG. 5, asgetting closer to the light exit surface 31. Both of the inclinedsurfaces 32A and 32B are symmetrical (for example, they are symmetricalabout the above-described axis of symmetry L1).

In the present embodiment, one of inclined surfaces 32 (the leftinclined surface 32A of the light guide plate 30 in FIG. 5) is arrangedto face the corresponding LED 16. More specifically, the inclinedsurface 32A is arranged to face the luminous surface 16 a of the LED 16,and is a light incident surface to which light enters from the LED 16.That is, the light guide plate 30 of the present embodiment has two ofthe inclined surfaces 32 on both sides of the Y-axis direction, andlight from the LED 16 enters from the one inclined surface 32A.

Transmission scattering units 35 transmitting and scattering light areformed on the nearly entire surface of the light exit surface 31. Thetransmission scattering units 35 are formed of a dot pattern. As shownin FIG. 6, for example, a plurality of dots 35 a with around shape in aplanar view is arranged in zigzags (stagger pattern, alternate pattern).The dots 35 a are formed by printing paste containing transparentparticles as transmission scattering materials (plastics or glasses)onto the light exit surface 31. This printing technique preferablyincludes silkscreen printing, ink jet printing and the like. Therefraction index of such transparent particles is set substantiallyequal to the refraction index of, for example, the light guide plate 30.Light in the light guide plate 30 is scattered by the transmissionscattering units 35. As a result, angle formed by light incident on thelight exit surface 31 generates light not beyond the critical angle(light not totally reflected), and light can be emitted externally fromthe light exit surface 31.

In the present embodiment, as shown in FIG. 6, an area of each of thedots 35 a (identified by a reference symbol 35 a 2 in FIG. 6) in the endpart Y1 on the side of the LED 16 in the Y-axis direction is formedsmaller than an area of the dots 35 a (identified by a reference symbol35 a 1 in FIG. 6) in the central portion in the Y-axis direction. In theY-axis direction (one side direction of the light exit surface 31) ofthe light exit surface 31, the distribution density of the transmissionscattering units 35 of the end part Y1 on the side of the LED 16 is setlower than the distribution density of the transmission scattering units35 on the center side in the Y-axis direction.

The distribution density of the transmission scattering units 35 may beset as described above by appropriately setting the arrangement intervalof the dots 35 a, other than changing the areas of the dots 35 a. Thetransmission scattering units 35 (dots 35 a) may be formed only on thecenter side without being formed in the end part Y1. As a result, thedistribution density of the transmission scattering units 35 of the endpart Y1 (light source side end part) on the side of the LED 16 may belower than the distribution density of the transmission scattering units35 on the center side. The end part Y1 on the side of the LED 16 is notlimited to the range shown in FIG. 6. Another configuration isapplicable, as long as the distribution density of the transmissionscattering units 35 is set relatively low on the side of the end part(outside) of the LED 16 side in the Y-axis direction, and thedistribution density thereof on the center side in the Y-axis directionis set relatively high.

According to the above-described configuration, light entered from theinclined surface 32A (light incident surface) of the light guide plate30 is totally reflected and guided in the light guide plate 30. Then,the light is scattered by the transmission scattering units 35 on thelight exit surface 31, thereby being emitted from the light exit surface31 (light emitted from the light exit surface 31 is identified by arrowsLC and LD in FIG. 7). The light emitted from the light exit surface 31is irradiated onto the back surface side of the liquid crystal panel 11.

The chassis 14 has a light reflection sheet 24 (reflection member) laidon the bottom plate 14 a thereof. The light reflection sheet 24 coversnearly the entire backside surface (a surface 33 opposite to the lightexit surface 31) of the light guide plate 30. The light reflection sheet24 is formed of, for example, a synthetic resin with a white frontsurface with excellent light reflectivity. The reflection sheet 24reflects light emitted thereon from the light guide plate 30 again ontothe light exit surface 31, thus enabling to increase the light useefficiency. Note that the material, color or the like of the lightreflection sheet 24 is not limited to the present embodiment, and anylight reflection sheet is applicable as long as it reflects light.

As described above, a plurality of light guide plates 30 is aligned inthe Y-axis direction along the bottom plate 14 a of the chassis 14 (seeFIG. 3). In the arrangement of the two adjacent light guide plates 30,the inclined surface 32 (for example, the inclined surface 32A in FIG.5) of one light guide plate 30 is oriented to the inclined surface 32(for example, the inclined surface 32B in FIG. 5) of the other lightguide plate 30. This arrangement forms the light source arrangement area36 in which the LED 16 is arranged between the adjacent inclinedsurfaces 32A and 32B.

As described above, the light guide plates 30 have a shape extending inthe X-axis direction (direction intersecting the above-described oneside direction (Y-axis direction) of the light exit surface 31). Asshown in FIG. 4, the light source arrangement area 36 also has a shapeextending in the X-axis direction in corresponding to the light guideplates 30. Along the extended direction (X-axis direction) of this lightsource arrangement area 36, the plurality of LEDs 16 is aligned. Inother words, the plurality of LEDs 16 is aligned over nearly the entirelength of the long side direction on the light guide plate 30. Theextended direction of the light guide plate 30 is not limited to theX-axis direction, and may be any direction as long as it “intersects theone side direction of the light exit surface”. The above-describedX-axis direction can be paraphrased as “a direction along a surfacedirection (X-axis and Y-axis directions) of the light exit surface andintersecting the one side direction of the light exit surface”.

As shown in FIG. 7, a length YB in the lower end part (end part of theback side) of the light source arrangement area 36 in the Y-axisdirection is set larger than a length YA of the upper end part (end partof the surface side, end part close to the light exit surface 31). Thatis, the light source arrangement area 36 has a trapezoidal shape in alateral view, and thus has its smallest part in the upper end part andhas a larger part toward the backside thereof.

The above-described optical members 15 (the diffuser plates 15 a and 15b) have an area sufficiently so as to cover the entire light guideplates 30 arranged on the chassis 14. The optical members 15 areconfigured to cover the entire light guide plates 30 at once from thelight exit surface 31 side (front side). The covered area includesspaces between the adjacent light guide plates 30 (spaces between thelight guide plates 30, areas corresponding to the upper end parts of thelight source arrangement areas 36).

Functions and effects of the present embodiment will be described next.In a process of manufacturing the backlight unit 12, the light guideplates 30 are assembled to the LED boards 17 on which the LEDs 16 aresurface-mounted. Specifically, after the LED boards 17 are set inpredetermined positions of the bottom plate 14 a of the chassis 14, thelight guide plates 30 are mounted in positions corresponding to therespective LEDs 16 on the LED boards 17.

At this time, the inclined surface 32 needs to be arranged toward thelight guide plate 30 in order to make light from the LED 16 enter thelight guide plate 30. The light exit surface 31 needs to be arrangedtoward the liquid crystal panel 11 in order to emit light from the lightguide plate 30 to the liquid crystal panel 11. That is, when thebacklight unit 12 is assembled, the light guide plate 30 needs to beorientated appropriately with respect to the LED 16.

In the present embodiment, of the side surfaces of the light guide plate30, two side surfaces are set as the inclined surfaces 32. The inclinedsurfaces 32 are inclined in a form protruding outside the light guideplate 30 in the Y-axis direction (one side direction of the light exitsurface 31), as getting closer to the light exit surface 31. In thisconfiguration, the light exit surfaces 31 and the surfaces 33 oppositeto the light exit surfaces 31 have different sizes in the light guideplates 30. This results in easy distinguishing between both surfaces, ascompared to a configuration where the light exit surfaces 31 and thesurfaces 33 opposite to the light exit surfaces 31 have the same size(for example, a configuration where the light guide plates 30 have arectangular parallelepiped shape). This realizes preferable workabilityin arranging the light exit surfaces 31 to be oriented toward apredetermined direction.

Further, both of the inclined surfaces 32A and 32B have symmetricalshapes with each other. Of the inclined surfaces 32A and 32B, whicheversurface may be used as the light entrance surface, and the same opticalcharacteristic can be generated between the both surfaces. When thelight guide plate 30 is arranged, either one of the two inclinedsurfaces 32A and 32B may simply be arranged to face the luminous surface16 a of the LED 16 (in the present embodiment, the inclined surface 32Ais facing the luminous surface 16 a). This realizes easer workability inarranging the light guide plate to be oriented toward the LED 16,compared to a configuration where only one surface of the light guideplate 30 is selected and is arranged to be oriented toward the LED 16.The inclined surfaces 32A and 32B may have asymmetrical shapes with eachother.

After the light guide plates 30 are installed onto the chassis 14 in anappropriate orientation, another member is assembled, thereby completingassembly of the backlight unit 12 and the liquid crystal display device10. Accordingly, in the present embodiment, it is possible to improvethe workability in assembling the light guide plate 30 onto the chassis14. This enables to provide the backlight unit 12 with improvedworkability in assembling the light guide plates 30, the liquid crystaldisplay device 10 including this backlight unit 12, and the televisionreceiver TV.

The light exit surface 31 has the transmission scattering units 35provided thereon. The units 35 transmit and scatter light in the lightguide plate 30, thereby emitting the light from the light exit surface31. The distribution density of the transmission scattering unit 35 onthe end part on the side of the LED 16 in the Y-axis direction is lowerthan the distribution density of the transmission scattering unit 35 onthe center in the Y-axis direction.

In the present embodiment, the inclined surface 32 is inclined in a formprotruding outside (the side of the LED 16) the light guide plate 30 inthe Y-axis direction, as getting closer to the light exit surface 31.Thus, as shown in FIG. 7, light entered the inclined surface 32A, whichis a light entrance surface is likely to be refracted toward the lightexit surface 31 (the refracted light is identified by an arrow LB). Theamount of light having a small incidence angle with respect to the lightexit surface 31 is increased at the end part on the side of the LED 16.As a result, on the light exit surface 31, the amount of light nottotally reflected (light to be emitted) is increased. If thedistribution density of the transmission scattering units 35 is equalover the entire surface of the light exit surface 31, an amount of lightto be emitted is increased on the end part on the side of the LED 16.Hence, the end part of the light exit surface 31 on the LED 16 side isbrighter than the center part, thus possibly resulting in unevenbrightness.

In the present embodiment, the distribution density of the transmissionscattering unit 35 on the end part on the side of the LED 16 in theY-axis direction is lower than the distribution density of thetransmission scattering unit 35 on the center side in the Y-axisdirection. Thus, an amount of light to be emitted is decreased in aposition with low density of the transmission scattering units 35 thanan amount of light to be emitted in a position with high densitythereof. Thus, an amount of light to be emitted is decreased on the endpart of the light exit surface 31 on the side of the LED 16. Even whenlight enters the inclined surface 32 with the inclined form as describedin this embodiment, it is possible to prevent a situation where anamount of light to be emitted is increased on the end part on the sideof the LED 16 than an amount of light to be emitted on the center side,thus preventing uneven brightness.

The transmission scattering units 35 are formed of a dot pattern. Inthis configuration, an aspect (area, arrangement interval) of the dots35 a is set, thus enabling to easily set the distribution density of thetransmission scattering units 35.

The light guide plate 30 has a shape extending in the X-axis direction(the direction intersecting one side direction of the light exit surface31). The plurality of LEDs 16 is aligned in this light guide plate 30 inthe X-axis direction. According to this configuration, the plurality ofLEDs 16 aligned along the X-axis direction is individually turned on,thereby controlling the brightness distribution in the X-axis direction.Thus configured light guide plates 30 and the LEDs 16 are aligned in theY-axis direction. In this configuration, a control board (not shown)controls whether or not each of the LEDs 16 is turned on, therebyenabling to control the brightness distribution in a planar direction(X-axis direction and Y-axis direction) on the light emission side ofthe backlight unit 12. This is so-called a local dimming technique. Thisenables to remarkably improve the contrast performance necessary in thedisplay performance of the liquid crystal display device 10.

According to this configuration (a configuration including the lightguide plates 30 extending in the X-axis direction and the LEDs 16aligned in the same direction), a smaller number of components is usedfor the light guide plate 30 than a configuration with a plurality oflight guide plates in the X-axis direction and LEDs 16 corresponding tothe light guide plates 30, resulting in preferable workability inassembling.

The lighting device further includes the chassis 14 housing the LEDs 16and the light guide plates 30. The plurality of LEDs 16 and light guideplates 30 are aligned along the bottom plate 14 a of the chassis 14. Oftwo adjacent light guide plates 30, the inclined surface 32A of onelight guide plate 30 is arranged to face the inclined surface 32B of theother light guide plate 30. The LED 16 is arranged in the light sourcearrangement area 36 formed between the inclined surface 32A of the onelight guide plate 30 and the inclined surface 32B of the other lightguide plate 30.

Accordingly, the LED 16 is arranged in the light source arrangement area36 formed between two adjacent light guide plates 30 arranged along thebottom plate 14 a of the chassis 14. Accordingly, in the backlight unit12, the size of the Z-axis direction (the direction intersecting thesurface (bottom surface) of the bottom plate 14 a of the chassis 14) canbe made small. That is, the plurality of light guide plates 30 arealigned, thereby realizing a local dimming technique and forming thethin backlight unit 12.

Further, the light source arrangement area 36 is formed by setting theinclined surface 32A of the one light guide plate 30 to face theinclined surface 32B of the other light guide plate 30. The upper endside (side near the light emission surface) of the light sourcearrangement area 36 is made smaller compared to a configuration wherethe light source arrangement area is formed between two surfacesparallel to each other. That is, in a planar view, the space (length YAof FIG. 7) between the light exit surfaces 31 of the adjacent lightguide plates 30 is made small, thus preventing uneven brightness thatmay occur in the space between the light exit surfaces 31.

If the light source arrangement area 36 is formed between the inclinedsurfaces 32A and 32B, the lower end (corresponding to the length YB ofFIG. 7) side (side far from the light exit surface 31) of the lightsource arrangement area 36 is easily made larger compared to aconfiguration where only one surface of two surfaces facing to eachother is inclined, the surfaces constituting the light sourcearrangement area 36. As a result, the light source arrangement area 36is easily made large, thus preventing remaining of heat generated whenthe LED 16 is turned on inside the light source arrangement area 36.This also prevents temperature from being raised in the LED 16, andenhances operational reliability.

The lighting device further includes the diffuser plates 15 a and 15 bcovering the space between the two adjacent light guide plates 30 fromthe light exit surface 31. In the backlight unit 12, it is possible tohave even brightness between the portion corresponding to the light exitsurface 31 of the light guide plate 30 and the portion corresponding tothe space between the light guide plates 30, and to prevent a darksection generated in the portion between the light guide plates 30.

A light source is the LED 16 (Light Emitting Diode). The LED is employedto make the power consumption lower.

The light reflection sheet 24 covers the surface 33 on the side oppositeto the light reflection surface 31, and reflects light from the LED 16onto the side of the light exit surface 31. With this configuration, thelight emitted from the light guide plate 30 to the side of the lightreflection sheet 24 is reflected again onto the light exit surface 31,thereby enhancing the light use efficiency.

Other Embodiment

The present invention is not limited to the above embodiments describedin the above description. The following embodiments may be included inthe technical scope of the present invention, for example.

(1) In the above-described embodiment, the Y-axis direction (short sidedirection of the chassis 14) has been described as the “one sidedirection of the light exit surface” byway of example. However, thepresent invention is not limited to this. For example, the X-axisdirection (long side direction of the chassis 14) may be the “one sidedirection of the light exit surface”. Alternately, an arbitrarydirection in a planar view along the X-axis direction and the Y-axisdirection may be applied.

(2) In the above-described embodiment, the transmission scattering units35 are formed on the light exit surface 31 of the light guide plate 30.This enables light to be emitted from the light exit surface 31.However, the present invention is not limited to this configuration. Forexample, a scattering reflection unit reflecting and scattering lightmay be formed on the surface 33 on the side opposite to the light exitsurface 31. The scattered and reflected light by this scatteringreflection unit may be emitted from the light exit surface 31.

(3) In the above-described embodiment, the dot pattern is printed,thereby forming the transmission scattering units 35. However, thepresent invention is not limited to this. For example, the transmissionscattering units 35 may simply transmit and scatter light, and the lightexit surface 31 may have a concave-convex surface or a lens-like form.

(4) The number of LEDs 16 and light guide plates 30 to be aligned andthe alignment direction are not limited to those of the above-describedembodiment, and changes may be made thereto.

(5) In the above-described embodiment, the diffuser plates 15 a and 15 bcover the entire light guide plates 30 arranged on the chassis 14.However, the present invention is limited to this. For example, thediffuser plates 15 a and 15 b may cover only a space between theadjacent light guide plates 30 from the side of the light exit surface31.

(6) In the above-described embodiment, three LED chips monochromaticallyemitting lights of R (Red), G (Green), and B (Blue) are combinedtogether, thereby forming the LEDs 16. However, the present invention isnot limited to this configuration. For example, the LED chipmonochromatically emitting light of blue may be embedded, and may emitlight of white color with a phosphor. It is possible to use any lightsource other than the LED.

(7) In the above embodiment, TFTs are used as switching components ofthe liquid crystal display device. However, the present invention isapplicable to liquid crystal display devices using switching componentsother than the TFTs (for example, thin-film diodes (TFD)), and alsoapplicable to liquid crystal display devices performing a black andwhite display other than liquid crystal display devices performing acolor display.

(8) In the above-described embodiment, the liquid crystal display deviceusing the liquid crystal panel 11 as a display panel has been describedas one example. However, the present invention is also applicable todisplay devices using different kinds of display panels.

(9) In the above-described embodiment, the television receiver includinga tuner has been described. However, the present invention is alsoapplicable to display devices without a tuner.

EXPLANATION OF SYMBOLS

-   -   10: Liquid crystal display device (Display device)    -   11: Liquid crystal panel (Display panel)    -   12: Backlight unit (Lighting device)    -   14: Chassis    -   14 a: Bottom plate of Chassis    -   15 a, 15 b: Diffuser plate    -   16: LED (Light source, light emitting diode)    -   16 a: Luminous surface    -   24: Light reflection sheet (Reflection member)    -   30: Light guide plate    -   31: Light exit surface    -   32: Inclined surface    -   32A: Inclined surface (Inclined surface opposite to luminous        surface of light source (Light entrance surface), and inclined        surface on one light guide plate)    -   32B: Inclined surface (Inclined surface of other light guide        plate) 33: Surface opposite to light exit surface on light guide        plate    -   35: Transmission scattering unit    -   36: Light source arrangement area    -   TV: Television receiver    -   Y1: End part of LED 16 (End part on light source side)

1. A lighting device comprising: a light source; and a light guide platehaving a light entrance surface through which light from the lightsource enters and a light exit surface through which the light exits,the light exit surface having a rectangular shape in a planar view,wherein the light guide plate has side surfaces at ends of one of sidesthereof, the side surfaces being configured as inclined surfaces thatare inclined toward the light exit surface of the light guide plate suchthat an end of the inclined surface on the light exit surface side isouter than another end of the inclined surface, and one of the inclinedsurfaces is configured as the light entrance surface that faces a lightemitting surface of the light source.
 2. The lighting device accordingto claim 1, wherein the inclined surfaces on the both sides havesymmetrical shapes with each other.
 3. The lighting device according toclaim 1, further comprising a transmission scattering member configuredto transmit and scatter light in the light guide plate such that thelight exits from the light exit surface, the transmission scatteringmember being arranged with lower distribution density in an area of thelight exit surface closer to the end of one of sides on the light sourceside than in an area of the light exit surface around a center withrespect to the one of sides.
 4. The lighting device according to claim3, wherein the transmission scattering member are formed of dotpatterns.
 5. The lighting device according to claim 1, wherein the lightguide plate has an elongated shape extending in a direction intersectingthe one of sides of the light exit surface, and the light sourceincludes a plurality of light sources arranged along the directionintersecting the one of sides of the light exit surface.
 6. The lightingdevice according to claim 1, further comprising a chassis housing thelight source and the light guide plate, wherein: the light sourceincludes a plurality of light sources and the light guide plate includeslight guide plates arranged along a bottom plate of the chassis; thelight guide plates are arranged such that the inclined surface of one ofthe adjacent light guide plates is opposite the inclined surface of theother one of the adjacent light guide plates; and the light sources arearranged in light source arrangement area between the inclined surfaceof the one of the adjacent light guide plates and the inclined surfaceof the other one of the adjacent light guide plates.
 7. The lightingdevice according to claim 6, further comprising at least one diffuserplate covering the adjacent light guide plates from the light exitsurface side.
 8. The lighting device according to claim 1, wherein thelight source is a light emitting diode.
 9. The lighting device accordingto claim 1, wherein the light guide plate has a surface opposite fromthe light exit surface covered by a light reflection member reflectingthe light from the light source toward the light exit surface.
 10. Adisplay device comprising: the lighting device according to claim 1; anda display panel configured to provide display using light from thelighting device.
 11. The display device according to claim 10, whereinthe display panel is a liquid crystal panel including liquid crystals.12. A television receiver comprising the display device according toclaim 10.